1. Field of the Invention
The present invention relates to a method for supplying hydrogen, for example, to high pressure hydrogen tanks mounted on vehicles and the like which use fuel cells.
2. Description of the Related Art
In these years, it has been investigated to use fuel cells as power source for vehicles and the like. In an above described vehicle which uses a fuel cell (hereinafter abbreviated as a fuel cell vehicle), a high pressure hydrogen tank is mounted on the vehicle for storing hydrogen used as fuel for the fuel cell.
Conventionally, rapid filling methods have been known as the method for supplying hydrogen to a high pressure hydrogen tank mounted on a fuel cell vehicle (see, for example, Japanese Patent Laid-Open No. 2002-89793).
As FIG. 4 shows, the above described rapid-filing method supplies hydrogen from a hydrogen supply means 3, comprising an in-station high pressure hydrogen tank HS 1 installed at a station and an on-off valve 2, to an in-fuel-cell-vehicle high pressure hydrogen tank HV 9 mounted on a fuel cell vehicle 8 by connecting a hydrogen duct 7 to the tank HV 9 by virtue of the pressure difference between these two tanks.
According to the method illustrated in FIG. 4, after the hydrogen duct 7 has been connected, the on-off valves 2, 10 are opened to start the hydrogen supply from the tank HS 1 to the tank HV 9, and the hydrogen supply is completed on equilibration between the hydrogen pressure in the tank HS1 and the hydrogen pressure in the tank HV 9.
However, the above described conventional method has a disadvantage that when hydrogen tries to be supplied up to the maximum filling pressure of the tank HV 9, the hydrogen pressure in the tank HS 1 which stores hydrogen, a flammable gas, becomes high and moreover a large storage amount of hydrogen is needed. Additionally, there is another disadvantage that the total amount of hydrogen contained in the tank HS 1 cannot be transferred to the tank HV 9 in such a way that when the hydrogen pressure in the tank HS 1 and the hydrogen pressure in the tank HV 9 become equilibrated with each other, some hydrogen remains untransferred in the tank HS 1.
Instead of adopting the method illustrated in FIG. 4, hydrogen may be supplied by a cascade method in which two or more tanks HS 1 are arranged and the two or more tanks HS 1 are successively changed over from one to another; however, in this connection, it has been known that at least one of these tanks HS 1 is required to have an initial hydrogen pressure of 42 MPa or more. Accordingly, the above described cascade method cannot offer any solutions to the above described problems.